Bad Astronomy

Saturn’s Thin Blue Line

I remember when I first looked through a telescope. I was four or five years old, and my dad bought a real el-cheapo department store ‘scope (A Tasco 40 mm for those keeping score at home). He set it up in the driveway, and pointed it at a star in the sky. When I looked through it, I saw it wasn’t a star, it was Saturn.

I still remember the amazement I felt (though the memory has dimmed with time, so I wonder now if the memory has been gilded with the emotions I have felt during the many times I have seen Saturn since). For a first-timer, nothing beats Saturn through a telescope. Nothing. It is a perfect jewel, a wonder floating in a sea of black. The rings are so obvious, and so geometrically wonderful. Whenever I show someone Saturn for the first time, they universally gasp in awe, and the most common thing I hear is “It looks just like it does in pictures!”

Saturn is a very cool place.

And the Cassini space probe just keeps hammering this point home, time and again. The images we’re getting from that machine are truly awe-inspiring. But there are so many! It’s returning thousands of images, far too many for the scientists to look at in real time.

Enter the internet. NASA did a smart thing: they put up a web page where they store every single raw image from Cassini. Anyone with access to the internet can browse these images, or download them and process them– the raw images are not in color, but with a little knowledge and practice, they can be combined to make color images.

That’s just what Spanish amateur astronomer Fernando Garcia Navarro did. He found some astonishing images of Saturn from Cassini, and combined them to form this jaw-dropper of an image:

Click the image to go to a higher-res image, or here for a super-high-res image.

For sheer beauty and awe-inspiring goodness, this is hard to beat. But wait! Where are the rings?

Look closely, and you’ll see them– they are edge-on, so they’re almost invisible (they’re the original “thin blue line”!). When Cassini crosses the plane of the rings, it sees them edge-on, and they nearly disappear. Saturn’s rings extend well over a half-million kilometers from the planet, making them comfortably bigger than the Moon’s orbit around the Earth… yet in most places they are less than a single kilometer thick! To give you an idea of just how thin this is, take a piece of paper and draw a circle on it 20 centimeters across (about 8 inches). If that circle represents Saturn’s rings, then to scale, that paper is 1000 times thicker than Saturn’s rings!

Amazing. Yet they still cast that magnificent shadow across the planet. And if that weren’t enough, two of Saturn’s moons can be seen in the image as well. And one other thing– most people spend so much time looking at the rings, that they never look at Saturn itself. In this image, you can see that Saturn is clearly non-spherical. It’s flattened, wider at the equator than at the poles, because it spins so rapidly (its day is only about 10 hours long) and also because it is very low density. These combine to make the planet 10% wider at the equator than at the poles!

I’ve said it before, and I’ll say it again– Saturn is a very cool place.